What Converting An Office Building To Housing Actually Requires
The obstacles are physical and regulatory, and the physical ones are decided by the shape of the building.
Converting office buildings to residential use is a recurring proposal for New York, and a genuine one — the city has done it before, extensively, in Lower Manhattan. It works for some buildings and not others, and which is which is largely settled by the original design.
Light and air
Residential use requires habitable rooms with adequate light and ventilation, which in practice means windows. Office floor plates built deep, with a large distance from the core to the exterior wall, produce interior space that cannot become a bedroom.
Buildings from earlier eras, designed before deep air-conditioned floor plates, convert far more readily. That is why the successful conversions cluster in older stock.
Plumbing
Office buildings concentrate plumbing in a central core. Residential buildings need it distributed to every unit. Running new risers through an existing structure is among the largest costs in a conversion and is sometimes the item that defeats the project.
Facades and windows
Sealed curtain wall systems designed for offices may not provide the openable windows or the thermal performance residential use expects, and replacing a facade is a project in itself.
The regulatory layer
Conversion requires the zoning to permit residential use, a new certificate of occupancy, and compliance with the building code provisions applying to residential occupancy — egress, fire separation, accessibility.
New York State and City have both adjusted rules to make conversions easier in defined circumstances, including provisions relating to older buildings and programs that pair conversion with affordability requirements. These change, and the applicable rules depend on the building's age and location.
The economics
A conversion competes with the building's value as an office. It becomes attractive when office value falls far enough relative to residential value to cover a very substantial construction cost.
That gap is the whole question, and it is why conversion proposals arrive in waves that follow the office market rather than housing need.